Interpreting englacial layer deformation in the presence of complex ice flow history with synthetic radargrams

Abstract

Fast ice flow on the Antarctic continent constitutes much of the mass loss from the ice sheet. However, geophysical methods struggle to constrain ice flow history at depth, or separate the signatures of topography, ice dynamics and basal conditions on layer structure. We develop and demonstrate a methodology to compare layer signatures in multiple airborne radar transects in order to characterize ice flow at depth, or improve coverage of existing radar surveys. We apply this technique to generate synthetic, along-flow radargrams and compare different deformation regimes to observed radargram structure. Specifically, we investigate flow around the central sticky spot of Whillans Ice Stream, West Antarctica. Our study suggests that present-day velocity flowlines are insufficient to characterize flow at depth as expressed in layer geometry, and streaklines provide a better characterization of flow around a basal sticky spot. For Whillans Ice Stream, this suggests that ice flow wraps around the central sticky spot, supported by idealized flow simulations. While tracking isochrone translation and rotation across survey lines is complex, we demonstrate that our approach to combine radargram interpretation and modeling can reveal critical details of past ice flow.

Five decades of radioglaciology

“…Examples include studies showing changes in ice-flow structure or folded stratigraphy in Greenland and entrained debris in a glacier in Patriot Hills, West Antarctica (Catania and others, 2006; Martín and others, 2009; Dahl-Jensen and others, 2013; Bell and others, 2014; Bingham and others, 2015; Kingslake and others, 2016; Winter and others, 2019; Ross and Siegert, 2020). Advances in processing radargrams to extract ice-sheet structure make it possible to interpret these features in regions of complex flow (Elsworth and others, 2020).…”

Inferring Ice Fabric From Birefringence Loss in Airborne Radargrams: Application to the Eastern Shear Margin of Thwaites Glacier, West Antarctica

“…While the COF of ice sheets are often directly quantified through thin‐section analyses from ice cores (e.g., Hansen & Wilen, 2002), the complex logistics of coring operations, as well as their scientific goals, have restricted the locations of these measurements to slow‐flowing (<50 m a −1 ) sections of ice sheets usually situated over domes and divides (e.g., Jouzel & Masson‐Delmotte, 2010). As such, these cores likely do not represent glaciologically dynamic areas that experience higher and more variable strain (Elsworth et al., 2020). In lieu of this constraint, ice‐penetrating radar has provided an alternative method to quantify bulk anisotropic COF patterns by exploiting the birefringence of polar ice, without the practical limitations of drilling (e.g., Hargreaves, 1977; Fujita et al., 2006; K. Matsuoka et al., 2012; Jordan et al., 2019; Young et al., 2020).…”

Noise Removal and Feature Extraction in Airborne Radar Sounding Data of Ice Sheets

“…At present, these radar data are extensively used to characterize the basal conditions of ice sheets [14,15] and to provide constraints in the extrapolation of englacial structures and processes [6,16,17]. Radar data are also used to evaluate ice flow dynamics [18,19], to calculate the basal roughness [20,21], to estimate heat flux and englacial temperature [22,23], to calculate basal reflectivity, and thus, to reveal subglacial lakes and hydrological drainages [24,25].…”